Ellipsometry is a versatile and powerful optical technique for the investigation of the physical properties of materials (e.g. a complex refractive index or dielectric function), including properties of thin films. Ellipsometry techniques can yield extremely accurate measurements, and certain ellipsometric measurement techniques provide unequaled capabilities for thin film metrology.
In contrast to ellipsometry, other measurement techniques (e.g. scanning electron microscopy, auger electron spectroscopy, transmission electron microscopy, X-ray photoemission spectroscopy, etc), while quite accurate, tend to require long set-up times, involved sample preparation, challenging (e.g. vacuum) environmental conditions, and are destructive to the sample. Spectroscopic Ellipsometry (SE), either variable wavelength or variable incidence angle, or both, however, is an optical technique, uses relatively low energy light sources, can be performed without physical contact with a sample, and accordingly is non-destructive in its application.
In general terms, an ellipsometer analysis changes in polarization of a probing light that is reflected off a sample. Ellipsometry can yield measurements pertaining to layers that are much thinner than the wavelength of the probing light itself, and ellipsometry can yield measurements that can then be used to calculate the complex refractive index of a thin film of material. In many practical applications (e.g. characterization of thin films, characterization of multi-layer semiconductor structures, etc), spectroscopic ellipsometry is commonly used to characterize film thickness for single layers or even the thicknesses of complex multilayer stacks ranging from a few angstroms or tenths of a nanometer to several micrometers.
In cases using a conventional ellipsometer, a sample containing the layers to be measured (e.g. a thin-film coated component, a silicon die, etc) is mounted in a location stationary to the ellipsometer apparatus, usually on a stage that is mechanically mounted to the ellipsometer apparatus. Thus movements of the apparatus also move the sample. However, for larger samples (e.g. sheets, rolls of fabric) it may be impractical or impossible to mechanically mount the ellipsometer apparatus to the sheet or fabric, or roll of material, or other large sample. Thus the sample-to-ellipsometer apparatus juxtaposition must be included in measurements. Moreover, measurements taken across the surface of the sheet or roll might each require calibration of the fabric-to-apparatus juxtaposition. In addition, conventional ellipsometers often require the sample to be mechanically mounted into the ellipsometer apparatus (e.g. the sample mounted onto a stage which is in turn affixed to the measurement system). In this configuration, existing ellipsometers have a fixed rotational axis for changing incidence and reflectance angle. For large samples, such as a 1 meter wide by 10 meter long sample of fabric, or, for continuously running samples such as a fiber tow, the measurement system has to be physically separated from the sample. Thus, new techniques are needed.
Other automated features and advantages of the present invention will be apparent from the accompanying drawings, and from the detailed description that follows below.